Close to 20 fire personal are being evaluated after they battled a blaze Friday night at a commercial building in southwest Fresno.

It happened around 10 p.m. Friday near Highway 99 and North Street. When crews entered the building barrels of hazardous materials exploded forcing a call out for a third alarm.

Firefighters were eventually able to get a handle on the blaze, but authorities said the situation could have been worse. "Life safety was a major concern looking at our folks we had unknown chemicals inside," Battalion Chief Todd Tuggle of the Fresno Fire Department said. "We had our folks exposed to that a very close proximity to the materials."Hazmat teams were called on scene to prevent exposure to the chemicals and firefighters who were exposed were treated and did not need to be transported to the hospital.

Investigators say materials inside the building used to make fire retardant overheated which caused the blaze and explosion.